How Super-Thick Smoothies May Help You Lose Weight

Protein isn’t the only thing that makes you feel full. Thickness, it turns out, can also do the trick.

A small new study published in the American Journal of Clinical Nutrition provides the perfect reason to dust off your blender and get whirling. Thickening a drink seems to make people feel fuller, regardless of how many calories it has. While the study did not look at weight loss specifically, it stands to reason thick drinks could play a useful role, since satiety is one of the main ways to prevent overeating.

Researchers from Wageningen University in the Netherlands asked 15 men to drink a series of four milkshakes. The only differences were their calorie contents—either 100 or 500 calories—and their viscosity—thin or thick.

After the men drank the shakes, they got MRI scans of their stomachs, which allowed researchers to determine the volume of the liquid there. For an hour and a half after ingestion, participants were asked every 10 minutes how full they felt.

Not surprisingly, the 100-calorie shakes were the fastest to leave the stomach. Adding fiber to the smoothie didn’t make it stay there longer, they found. But the shake’s viscosity—not the number of calories it had—was what made the men report feeling full. In fact, people who drank the thick 100-calorie shake felt even fuller than people who drank the thin 500-calorie shake.

The study authors dubbed this effect “phantom fullness”: being more satiated because of a food’s thickness, not its energy density. It’s bad news for anyone who hopes the calories in a sugary soda or juice will tide over their hunger pangs; without that satisfying thickness, you’re likely to leave hungry. But the results are useful for those of us who like our drinks thick, whether they’re milkshakes, smoothies or—we hope—chunky tropical cocktails.

More research is needed to determine which types of fiber or thickeners will do the trick. But if drinking something thicker makes you feel fuller, that may nudge you eat fewer calories afterward.